Transmission

Abstract

A transmission includes a transmission mechanism. The transmission mechanism includes a planetary gear mechanism and a fixing element. A ring gear is provided with a first gear meshing with an output gear on an output member and a second gear meshing with a plurality of pinion gears. The output gear and the first gear include helical gears meshing with each other. The second gear and the plurality of pinion gears include helical gears meshing with each other. Helix angles of the output gear and the first gear and helix angles of the second gear and the plurality of pinion gears are set so that a thrust force generated in a case where the output gear and the first gear rotate and a thrust force generated in a case where the second gear and the plurality of pinion gears rotate are directed towards each other.

What is claimed is: 
     
       1. A transmission provided with a transmission mechanism that changes a speed of rotation generated by a driving force input from a driving source and that outputs the rotation to an output member, the transmission comprising:
 the transmission mechanism including
 a planetary gear mechanism including a sun gear, a ring gear, a carrier, and a plurality of pinion gears, the plurality of pinion gears being rotatably supported by the carrier and being meshed with the sun gear and the ring gear, and 
 a fixing element that switches the carrier between a state in which the carrier is allowed to relatively rotate with respect to a member on a fixation side and a state in which the carrier is fixed with respect to the member on the fixation side; 
 
 the ring gear having a first gear that meshes with an output gear on the output member and a second gear that meshes with the pinion gears; 
 the output gear and the first gear being constituted by helical gears that mesh with each other; 
 the second gear and the pinion gears being constituted by helical gears that mesh with each other; 
 helix angles of the output gear and the first gear and helix angles of the second gear and the pinion gears being set so that a thrust force generated when the output gear and the first gear rotate and a thrust force generated when the second gear and the pinion gears rotate are directed towards each other; and 
 a first meshing point where the output gear and the first gear mesh with each other and a second meshing point where the second gear and one of the pinion gears mesh with each other being arranged on a straight line that connects a rotation center of the output member and a rotation center of the planetary gear mechanism due to the operation of the fixing element to fix the carrier. 
 
     
     
       2. The transmission according to  claim 1 , wherein
 the fixing element includes
 a first member that is attached to the member on the fixation side, 
 a second member that is attached to the carrier, 
 a single or a plurality of first groove portions that are formed in a first surface of the first member, the first surface opposing the second member, 
 a single or a plurality of second groove portions that are formed in a second surface of the second member, the second surface opposing the first surface, 
 an engagement element that is received in the single or the plurality of first groove portions or the single or the plurality of second groove portions, the engagement element having an end connected to the first member or to the second member, and 
 a biasing element that biases the engagement element in a direction that protrude the engagement element toward the single or the plurality of first groove portions or the single or the plurality of second groove portions, the biasing element having a first end connected to the first member or the second member and a second end connected to the engagement element, 
 
 when the second member is about to relatively rotate in one direction with respect to the first member, the engagement element engages with the single or the plurality of first groove portions or the single or the plurality of second groove portions so as to restrict relative rotation, 
 when the second member is about to relatively rotate in another direction with respect to the first member, the engagement element is received in the single or the plurality of second groove portions or the single or the plurality of first groove portions so as to permit relative rotation, 
 at least one of the single or the plurality of first groove portions is disposed at a position that is the same as a position of the first meshing point in a rotating direction, and 
 each of the single or the plurality of second groove portions is disposed at a position that is the same as a position of a corresponding one of the plurality of pinion gears in the rotating direction. 
 
     
     
       3. A transmission comprising:
 a transmission mechanism to change a speed of rotation generated by a driving force input from a driving source and to output the rotation to an output member, the transmission mechanism comprising:
 a planetary gear mechanism including a sun gear, a ring gear, a carrier, and a plurality of pinion gears, the plurality of pinion gears being rotatably supported by the carrier and being meshed with the sun gear and the ring gear, the ring gear having a first gear meshing with an output gear on the output member and a second gear meshing with the plurality of pinion gears, the output gear and the first gear comprising helical gears meshing with each other, the second gear and the plurality of pinion gears comprising helical gears meshing with each other, helix angles of the output gear and the first gear and helix angles of the second gear and the plurality of pinion gears being set so that a thrust force generated in a case where the output gear and the first gear rotate and a thrust force generated in a case where the second gear and the plurality of pinion gears rotate are directed towards each other; and 
 a fixing element to switch the carrier between a state in which the carrier is allowed to relatively rotate with respect to a member on a fixation side and a state in which the carrier is fixed with respect to the member on the fixation side, a first meshing point where the output gear and the first gear mesh with each other and a second meshing point where the second gear and one of the plurality of pinion gears mesh with each other being arranged on a straight line connecting a rotation center of the output member and a rotation center of the planetary gear mechanism due to the operation of the fixing element to fix the carrier. 
 
 
     
     
       4. The transmission according to  claim 3 ,
 wherein the fixing element comprises:
 a first member attached to the member on the fixation side; 
 a second member attached to the carrier; 
 a single or a plurality of first groove portions provided in a first surface of the first member, the first surface opposing the second member; 
 a single or a plurality of second groove portions provided in a second surface of the second member, the second surface opposing the first surface; 
 an engagement element received in the single or the plurality of first groove portions or the single or the plurality of second groove portions, the engagement element having an end connected to the first member or the second member; and 
 a biasing element to bias the engagement element in a direction that protrudes the engagement element toward the single or the plurality of first groove portions or the single or the plurality of second groove portions, the biasing element having a first end connected to the first member or the second member and a second end connected to the engagement element, 
 
 wherein in a case where the second member relatively rotates in one direction with respect to the first member, the engagement element engages with the single or the plurality of first groove portions or the single or the plurality of second groove portions so as to restrict relative rotation, 
 wherein in a case where the second member relatively rotates in another direction with respect to the first member, the engagement element is received in the single or the plurality of second groove portions or the single or the plurality of first groove portions so as to permit relative rotation, 
 wherein at least one of the single or the plurality of first groove portions is disposed at a position that is a same as a position of the first meshing point in a rotating direction, and 
 wherein each of the single or the plurality of second groove portions is disposed at a position that is a same as a position of a corresponding one of the plurality of pinion gears in the rotating direction. 
 
     
     
       5. The transmission according to  claim 1 ,
 wherein the first gear and the second gear are respective outer and inner surfaces of the ring gear. 
 
     
     
       6. The transmission according to  claim 1 ,
 wherein the fixing element is disposed on the straight line that connects the rotation center of the output member and the rotation center of the planetary gear mechanism when the carrier is fixed with the fixing element. 
 
     
     
       7. The transmission according to  claim 1 ,
 wherein the first meshing point and the second meshing point are arranged at a same position in a circumferential direction of the planetary gear mechanism when the carrier is fixed with the fixing element. 
 
     
     
       8. The transmission according to  claim 3 ,
 wherein the first gear and the second gear are respective outer and inner surfaces of the ring gear. 
 
     
     
       9. The transmission according to  claim 3 ,
 wherein the fixing element is disposed on the straight line that connects the rotation center of the output member and the rotation center of the planetary gear mechanism when the carrier is fixed with the fixing element. 
 
     
     
       10. The transmission according to  claim 3 ,
 wherein the first meshing point and the second meshing point are arranged at a same position in a circumferential direction of the planetary gear mechanism when the carrier is fixed with the fixing element.